New Study Of Twins Examines Nature Vs. Nurture

A landmark study on identical twins reared apart offers reassurance to parents who worry about the adequacy of their child-rearing efforts and rekindles the age-old debate of nature vs. nurture.

The long-awaited study, the most definitive in a long series trying to separate the effects of genetics and environment in a child`s development, comes down heavily on the side of genetics.

It indicates that the broad outlines of personality and behavior are put in place in the brief instant when the mother`s and father`s genes mix during conception, establishing the basic route that the child will take during the rest of its life.

Nurture -- the family environment -- plays a much smaller role, according to the study, published today in the journal Science.

``For most every behavioral trait so far investigated, from reaction time to religiosity, an important fraction of the variation among people turns out to be associated with genetic variation,`` wrote the University of Minnesota researchers, led by psychologist Thomas J. Bouchard, Jr.

This work ``does not show that parents cannot influence those traits, but simply that this does not tend to happen in most families.``

Psychologist Robert Plomin of the Pennsylvania State University called the Minnesota twin study ``the single most important finding in behavioral genetics in the last decade.`` The results in general agree with many previous studies of the role of genetics in producing behavior.

But the new research finds a stronger connection between genetics and behavior than the previous studies, said Norman Krasnegor of the National Institute of Child Health and Human Development.

``It`s a powerful statement and one which people will debate for a long time,`` he said. ``It will cause some good controversy and make people work to come up with new data or alternate explanations.``

Psychologist David Rowe of the University of Arizona agreed heartily with the new study. ``Parents probably deserve less credit for when things go well, and much less blame for problems,`` he said.

But the study ``does not imply that parenting is without lasting effects,`` the group wrote. ``Parents can produce ... effects if they grossly deprive or mistreat all their children. It seems reasonable that charismatic, dedicated parents determined to make all their children share certain personal qualities, interests, or values, may sometimes succeed.``

Three previous studies of such twins have been conducted, but the Minnesota study, begun in 1979, is by far the largest, now enrolling more than 100 sets from around the world.